Tantalum tertiary amylimido tris (dimethylamide), a process for producing the same, a solution of starting material for mocvd using the same, and a method of forming a tantalum nitride film using the same

ABSTRACT

A stable compound having a vapor pressure higher by 1 order than that of Ta(NtBu)(NEt 2 ) 3  is provided as a starting material for forming a TaN film as a barrier film by the CVD method. There are further provided a process for producing the same and a method of forming a TaN film by using the same. The novel compound, tantalum tertiary amylimido tris(dimethylamide) [Ta(NtAm)(NMe 2 ) 3 ] has a vapor pressure of 1 Torr at 80° C., and its melting point is 36° C. This compound is obtained by allowing 1 mole of TaCl 5 , 4 moles of LiNMe 2  and 1 mole of LiNHtAm to react with one another in an organic solvent in the vicinity of room temperature, then separating byproducts by filtration, distilling the solvent away, and distilling the product in vacuo. This compound can be used as a starting material in CVD to form a cubic TaN film on a SiO 2 /Si substrate at 550° C. at 0.05 Torr.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tantalum compound suitable forforming, by the MOCVD method, a tantalum nitride film serving as aground barrier in forming a copper film on semiconductor devices, aprocess for producing the same, and a method of forming a tantalumnitride film using the same.

2. Description of the Related Art

It is known that tantalum nitride is very effective as a ground barrieron semiconductor devices. For further thinning copper paths for electriccurrent, further thinning of this barrier film is also required, andformation of a tantalum nitride film by the CVD method superior inmass-productivity and in the step coverage ability came to be necessary.

U.S. Pat. No. 5,668,054 discloses a CVD method using tantalum tertiarybuthylimido tris(diethylamide) Ta(NtC₄H₉)(N(C₂H₅)₂)₃ (referred tohereinafter as Ta(NtBu)(NEt₂)₃ as the starting material, wherein alow-resistant tantalum nitride film is formed on a substrate at 450 to650° C. in a low-pressure reaction chamber of cold wall type at 0.02Torr. The film at 600° C. is preferable with resistance as low as 600μΩ·cm, and even upon treatment at a high temperature of 500° C., canprevent copper diffusion and significantly lower leak current.

The starting material Ta(NtBu)(NEt₂)₃ is liquid at room temperature, andis supplied after gasification by heating at a source temperature of 40to 50° C.

In Appl. Phys. Lett., vol. 67(8)1128 (1995), the inventors of said priorart patent estimated that low-resistant cubic TaN could be formedbecause Ta═NtBu in the starting compound, that is, the strong bond ofTa═N was preserved and integrated in the cubic system. Beforepublication of said literature, said inventors disclosed in J. Mater.Sci. Lett., vol. 11, 96 (1992) that low-carbon cubic TaN was formed byCVD of Ta(NEt)(NEt₂)₃, but because a pure material of Ta(NEt)(NEt₂)₃ washardly obtained, said inventors used Ta(NtBu)(NEt₂)₃ in place ofTa(NEt)(NEt₂)₃.

R. M. Fix, R. G. Gordon and D. M. Hoffman, in Chem. Mater., vol. 5, 614(1993), have reported that cubic Ta₃N₅ film of high resistance (>10⁶μΩ·cm) was formed in CVD using tantalum pentakis(dimethylamide)[Ta(NMe₂)₅] and ammonia.

U.S. Pat. No. 6,015,917 claims 10 groups of compounds having Ta—N and/orTa═N bond as the starting material in CVD for forming a tantalum nitridefilm, as well as solutions thereof in hexane or toluene. In (viii),claim 1 describes, but does not specify, Ta(NR₁)(NR₂R₃)₃ wherein R₁, R₂and R₃ are independently from H, C₁-C₈ alkyl, aryl, C₁-C₈perfluoroalkyl, and silicon-containing groups selected from the groupconsisting of silane, alkyl silane, perfluoroalkylsilyl, triaryl silaneand alkylsilyl silane. This patent specification describes, in theExamples, only one compound of tantalum pentakis(dimethylamide)[Ta(NMeEt)₅], and does not contain any description of the conditions forforming the film and the physical properties of the film.

JP-A 2000-204095 also discloses that a tantalum nitride film was formedfrom Ta(NMeEt)₅ or a solution thereof in organic solvent and an ammoniagas at a substrate temperature of 450° C. at a pressure of 10 Torr, butthere is no description of the crystalline form of said film.

As described above, low-resistant cubic TaN has been obtained until nowfrom only tantalum alkylimido tris(dialkylamide) having Ta═N.

It is generally preferable that at the time of supply, the startingcompound in CVD for mass-production has such properties that it is apure material, has high vapor pressure, is thermally stable at the timeof supply, and is liquid in the vicinity of room temperature or at leastat the temperature of a source used. From these viewpoints,Ta(NtBu)(NEt₂)₃ in U.S. Pat. No. 5,668,054 is disadvantageous in thatits vapor pressure is not high because of high molecular weight.According to measurement of vapor pressure by the present inventors, thevapor pressure thereof was 1 Torr/130° C.

According to measurement of vapor pressure by the present inventors, asimilar known compound, tantalum tertiary buthylimidotris(dimethylamide) [Ta(NtC₄H₉)(N(CH₃)₂)₃] has a vapor pressure of 1Torr/70° C. which is higher than that of Ta(NtBu)(NEt₂)₃, but theproblem of this compound is its melting point as high as 69° C. For ausual liquid mass flow controller, the temperature which can be kept byheating for melting a starting compound is about 50° C., and thusTa(NtBu)(NMe₂)₃ with a melting point of 69° C. is not suitable. Thematerial desirably has a melting point in the vicinity of roomtemperature or about 40° C. or less.

SUMMARY OF THE INVENTION

The present invention provides a novel compound having a higher vaporpressure than that of Ta(NtBu)(NEt₂)₃, a melting point of 40° C. orless, and Ta═N bond, as well as a process for producing the same.Further, the present invention provides a method of forming a cubic TaNfilm by using the same in the CVD method.

According to one aspect of the present invention, there is provided anovel compound, tantalum tertiary amylimido tris (dimethylamide).

According to another aspect of the present invention, there is provideda process for producing tantalum tertiary amylimido tris(dimethylamide),which comprises allowing 1 mole of tantalum pentachloride, 4 moles oflithium dimethylamide and 1 mole of lithium tertiary amylamide to reactwith one another in an organic solvent, then separating a byproductlithium chloride by filtration, distilling the solvent away, anddistilling the residue in vacuo.

According to still another aspect of the present invention, there isprovided a solution of starting material for MOCVD, comprising at least10 wt % organic solvent added to tantalum tertiary amylimidotris(dimethylamide).

According to still another aspect of the present invention, there isprovided a method of forming a tantalum nitride film by the MOCVD methodwherein tantalum tertiary amylimido tris (dimethylamide) is used as thestarting material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the result of measurement of Ta(NtAm)(NMe₂)₃ by EI-MS.

FIG. 2 shows the result of measurement of Ta(NtAm)(NMe₂)₃ by ¹H-NMR.

FIG. 3 shows the result of measurement of Ta(NtAm)(NMe₂)₃ by FT-IR.

FIG. 4 shows the result of measurement of Ta(NtAm)(NMe₂)₃ by TG-DTA at 1atmospheric pressure.

DETAILED DESCRIPTION OF THE INVENTION

The tantalum tertiary amylimido tris(dimethylamide) of the presentinvention is a novel compound (referred to hereinafter asTa(NtAm)(NMe₂)₃. This compound can be produced according to a processfor producing Ta(NtBu)(NMe₂)₃ as described by William A. Nugent, Inorg.Chem., vol. 22, 965 (1983).

Four moles of lithium dimethylamide and 1 mole of lithium tertiaryamylamide are suspended and dissolved in hexane, and powdery tantalumpentachloride is added thereto under stirring and cooling with water,and the mixture is reacted for 2 days at 10 to 40° C. Then, lithiumchloride crystals formed as byproduct are removed by filtration, andfrom the resulting yellow liquid, low-boiling components such as solventetc. are distilled away under reduced pressure. As a result, an orangeviscous liquid remains, and this product is distilled under reducedpressure at 1 Torr, whereby a yellow liquid is obtained in the vicinityof 90° C. This liquid is recrystallized from hexane at −30° C., and theresulting pale yellow crystals are subjected to distillation in vacuo at1 Torr, and a pale yellow liquid is obtained as a major distillate atabout 80° C. This liquid turns pale yellow solid at room temperature.The yield is 61% based on tantalum pentachloride.

Lithium dimethylamide used as the starting material is obtained in awhite-yogurt state by reacting a solution of n-butyl lithium in hexanewith a dimethylamine gas. Lithium tert-amylamide is obtained in awhite-suspension form by reacting a solution of n-butyl lithium inhexane with tert-amylamine. These two reaction solutions may be combinedfor use. As the reaction solvent, it is possible to use not only hexanebut also heptane, octane, toluene, diethyl ether and THF.

If tantalum pentachloride used is a high-purity commercial product, thefinally formed product has less impurities of metal elements. As amatter of course, the reaction rate and the increase in the reactiontemperature are influenced depending on the grain size of tantalumpentachloride, and thus the rate of adding the same is regulated. Thereaction time is 5 to 50 hours.

One mole of tantalum pentachloride is charged with 4 moles of lithiumdimethylamide and 1 mole of lithium tert-amylamide, but lithiumdimethylamide and lithium tert-amylamide may be added in slight excess.

The identification results and physical properties of Ta(NtAm)(NMe₂)₃obtained in Example 1 are described below.

(1) Analysis of the Composition

The result of ICP atomic emission spectroscopic analysis of a solutionformed by decomposing the compound in a wet system is as follows:

Found: 45.9 wt % Ta (theoretical: 45.4 wt %) Analysis of C, H, and N: C:32.8 (theoretical, 33.2 wt %), H: 7.2 (theoretical, 7.4 wt %), N: 13.5(theoretical, 14.1 wt %),

(2) Analysis of Impurities

The result of ICP emission spectroscopic analysis (unit: ppm) is asfollows:

Al<1, Ca<1, Fe<1, Mg<1, Ti<1, and Li<1, thus indicating high purity.

Analysis of total Cl indicated that Cl was 4 ppm.

(3) EI-MS

Measurement Conditions

Unit: JEOL AX505W

Ionization method: EI

Ionization-source temperature: 230° C.

Ionization energy: 70 eV

The measurement result is shown in FIG. 1.

There are two isotopes of Ta, but taking it into consideration that99.99% is ¹⁸¹Ta, major m/z values and their corresponding strength (%)and ion species are shown below: m/z=411 (12%) Ta [NC(CH₃)₂C₂H₅][N(CH₃)₂]₂ [N(CH₃)(C₂H₅)] or Ta [NC(CH₃)₂CH(CH₃)₂] [N(CH₃)₂]₃

398 (7%) Ta [NC(CH₃)₂C₂H₅] [N(CH₃)₂]₃ molecular ion

383 (10%) Ta [NC(CH₃)C₂H₅] [N(CH₃)₂]₃

369 (47%) Ta [NC(CH₃)₂] [N(CH₃)₂]₃

58 (58%) C₄H₁₀ or N(CH₃)(C₂H₅)

44 (100%) N(CH₃)₂

(4) ¹H-NMR

Measurement conditions:

Unit: BRUKER AC300P (300 MHz)

Solvent: C₆D₆

Method: 1D

The measurement result is shown in FIG. 2.

δ_(H) (ppm) and (assignment) are shown below: 3.31 s (18H, N(CH ₃)₂),2.30 d (1.5H, not clear), 1.75 q (2.4H, CH₃CH ₂C(CH₃)₂N), 1.49 s (7.9H,CH₃CH₂C(CH ₃)₂N), 1.30 t (3.8H, CH ₃CH₂C(CH₃)₂N),

(5) FT-IR

Measurement conditions:

Unit: SHIMADZU FT-IR8600

Method: KBr method

Resolution: 4.0 cm⁻¹

The measurement result is shown in FIG. 3. Spectrum (cm⁻¹):

3655, 2964, 2916, 2855, 2824, 2775, 2397, 2349, 1462, 1423, 1371, 1352,1319, 1298, 1252, 1215, 1178, 1151, 1130, 1057, 1040, 1024, 1001, 968,949, 907, 768, 652, 550

(6) Vapor Pressure

1 Torr/80° C. from data on distillation thereof.

(7) State and Melting Point

It was pale yellow crystals and its melting point was 36° C.

(8) TG-DTA

Measurement conditions:

Sample weight: 12.51 mg

Atmosphere: Ar, 1 atmospheric pressure

Heating rate: 20.0 deg/min

The measurement result is shown in FIG. 4.

(9) Conversion Thereof into a Solution

Ta(NtAm)(NMe₂)₃ was completely dissolved in hexane at 20° C. to give 10wt % organic solvent solution without forming any precipitates. Thiscompound was dissolved in toluene as well in the same manner as above.

This compound was identified as Ta(NtAm)(NMe₂)₃ on the basis of theresults of mainly the determined composition and analysis thereof byEI-MS, ¹H-NMR and FT-IR described above.

Then, the known compounds Ta(NtBu)(NEt₂)₃ and Ta(NtBu)(NMe₂)₃ weresynthesized in the same manner as for Ta(NtAm)(NMe₂)₃, and their meltingpoint and vapor pressure were determined and compared with those of thepresent compound Ta(NtAm)(NMe₂)₃.

The results of melting point and vapor pressure are shown in Table 1.

TABLE 1 Temperature Compound Melting point (° C.) (° C.) giving 1 TorrTa(NtAm)(NMe₂)₃ 36 80 Ta(NtBu)(NEt₂)₃ Liquid at room temp. 130Ta(NtBu)(NMe₂)₃ 69 70

As can be seen from Table 1, the temperature at which theTa(NtAm)(NMe₂)₃ of this invention gives 1 Torr is 80° C. which is lowerby about 50° C. than 130° C. for Ta(NtBu)(NEt₂)₃. Further, the vaporpressure of Ta(NtBu)(NEt₂)₃ at 80° C. is as low as 0.1 Torr, and whencompared at the same temperature, the vapor pressure of theTa(NtAm)(NMe₂)₃ of this invention is about 10 times as high as that ofTa(NtBu)(NEt₂)₃. Accordingly, it is evident that as the startingmaterial in CVD, the Ta(NtAm)(NMe₂)₃ of this invention has verypreferable properties in respect of vapor pressure. Therefore, thepresent compound can be vaporized at a lower source temperature and at alower temperature of a gasification unit, thus undergoing less heatdeterioration, being stable during use and reducing particles generated.

As can be seen from the result of TG-DTA in FIG. 4, the Ta(NtAm)(NMe₂)₃of this invention is well gasified, and thus the residue remaining aftervaporization is as low as 13.3% at 450° C., and thus the compound isrelatively stable to heat.

According to the result of EI-MS in FIG. 1, there is a major peak of afragment with m/z=369 estimated to contain Ta═N bond, suggesting thatthe present compound forms TaN relatively easily.

The Ta(NtAm)(NMe₂)₃ of this invention is of high purity with 1 ppm orless metal element impurities and 4 ppm Cl. Its melting point is 36° C.which is slightly higher than room temperature, so that attention shouldbe paid so as not to solidify the compound. Its purity can be furtherraised by refining through distillation.

The present invention also relates to a method of forming a tantalumnitride film by the MOCVD method, wherein Ta(NtAm)(NMe₂)₃ is used as thestarting material.

The method of feeding Ta(NtAm)(NMe₂)₃ is as follows:

{circle around (1)} While the source temperature is kept at 50 to 120°C., the compound is fed at the self-pressure of its generated vapor by avapor source mass flow controller;

{circle around (2)} Ta(NtAm)(NMe₂)₃ is liquefied by keeping the sourcetemperature at a temperature higher than the melting point of 36° C.,preferably at 40° C. or more, followed by gasification thereof bybubbling with a carrier gas;

{circle around (3)} The compound is liquefied by increasing the sourcetemperature to 40° C. or more, and the resultant liquid is fed by aliquid mass flow meter heated at about 50° C. and then gasified in agasification unit; and

{circle around (4)} Ta(NtAm)(NMe₂)₃ is dissolved at room temperature in10 wt % or more organic solvent, and the resultant solution is fed by aliquid mass flow controller or a liquid flow mass flow meter at roomtemperature, and then gasified in a gasification unit.

Ta(NtAm)(NMe₂)₃ in a liquid form has a viscosity of 10 to 20 cp, towhich bubbling, a mass flow controller or a mass flow meter can beapplied. The organic solvent in {circle around (4)} can make use ofconventional solvents for use in the starting material in CVD, such ashexane, heptane, octane and butyl acetate.

The substrate can make use of SiO₂/Si to form copper paths for electriccurrent thereon.

The tantalum nitride film can be formed by thermal CVD whereinTa(NtAm)(NMe₂)₃ is brought into contact with a substrate at atemperature of 450 to 650° C. under reduced pressure at 10⁻² to 1 Torr.The tantalum nitride film obtained on the substrate having a highertemperature is cubic TaN according to XRD. Accordingly, it is lowresistant. Adhesion of the tantalum nitride film to the SiO₂/Sisubstrate is also good. Only Ta(NtAm)(NMe₂)₃ may be introduced into theCVD chamber, but if necessary an ammonia gas may be supplied.

EXAMPLES Example 1 Production of Ta(NtAm)(NMe₂)₃

A 500-mL three-necked Erlenmeyer flask equipped with a thermometer and astirrer was evacuated and replaced therein by an argon atmosphere, and150 mL fresh LiNMe₂ suspension in hexane (20.4 g or 0.40 mol LiNMe₂) and50 mL fresh LiNHtAm suspension in hexane (9.3 g or 0.10 mol LiNHtAm)were introduced into the flask and stirred well for 1 hour. While theflask was cooled with water, powdery high-purity TaCl₅ (35.8 g, 0.10mol) was gradually added thereto such that the temperature of thereaction solution became 20 to 35° C. Thereafter, the mixture wasstirred at room temperature for 48 hours, to form slurry with goodsedimentation properties. After LiCl particles formed as byproduct wereseparated by filtration, a yellow transparent liquid was obtained. Thisliquid became an orange viscous liquid by allowing the solvent hexaneand amines formed as byproducts to be distilled away under reducedpressure on an oil bath at a temperature of 30° C. This liquid wassubjected to distillation at about 90° C. at 1 Torr to give 28.3 gyellow transparent liquid. This liquid was dissolved in 30 ml hexane andre-crystallized therefrom at −30° C. The resulting pale yellow crystalswere subjected to distillation at 1 Torr, and 24.3 g colorless liquidwas obtained as a major distillate at a distilling temperature of about80° C. This liquid was solidified at room temperature into pale yellowneedle crystals. As a result of identification as described above, theresultant product was Ta(NtAm)(NMe₂)₃ (0.061 mol) and the yield was 61%based on TaCl₅.

Example 2 Formation of TaN Film by CVD Method Using Ta(NtAm)(NMe₂)₃

A cylinder containing Ta(NtAm)(NMe₂)₃ obtained in Example 1 was heatedat 110° C., and the generated vapor was introduced at the self-pressurethereof via a vapor source mass flow controller into a CVD chamber ofcold wall type. The CVD chamber was kept at 0.05 Torr in an exhaustsystem, and the vapor was thermally decomposed and accumulated on aSiO₂/Si substrate at 550° C. After an about 100-nm film was formed, thefilm was measured with XRD, indicating that the film was cubic TaN.

Example 3

In Example 2, a cylinder containing Ta(NtAm)(NMe₂)₃ was kept at 50° C.to liquefy the Ta(NtAm)(NMe₂)₃, then the resultant liquid was introducedvia a liquid mass flow meter heated and kept at 50° C., and the whole ofthe liquid was gasified in a gasification unit at 120° C. and thenintroduced into a CVD chamber. The same procedure as in Example 2 wasconducted in the subsequent process, whereby a cubic TaN film could beformed.

Example 4

Ta(NtAm)(NMe₂)₃ was converted at room temperature into a solution byadding 10 wt % hexane, then the resultant solution was introduced via aliquid mass flow controller, and the whole of the solution was gasifiedin a gasification unit at 120° C. and then introduced into a CVDchamber. The same procedure as in Example 2 was conducted in thesubsequent process, whereby a cubic TaN film could be formed.

INDUSTRIAL APPLICABILITY

The Ta(NtAm)(NMe₂)₃ of the present invention is a novel compound havinga vapor pressure that is 10 times as high as that of knownTa(NtBu)(NEt₂)₃ at the same temperature.

Accordingly, the present compound can supply a large amount of vaporeasily in mass-production CVD. This compound can be easily purified tohigh degrees by re-crystallization and distillation, and thus it ispreferable as a starting material in CVD for semiconductor devices. Inaddition, this compound has a melting point of 36° C., and therefore itcan be liquefied by slight heating and thus stably supplied by a liquidmass flow controller.

By subjecting this Ta(NtAm)(NMe₂)₃ on a SiO₂/Si substrate to thermalCVD, a cubic TaN film of low resistance can be formed.

What is claimed is:
 1. Tantalum tertiary amylimido tris(dimethylamide).2. A process for producing tantalum tertiary amylimidotris(dimethylamide), which comprises allowing 1 mole of tantalumpentachloride, 4 moles of lithium dimethylamide and 1 mole of lithiumtertiary amylamide to react with one another in an organic solvent, thenseparating a byproduct lithium chloride by filtration, distilling thesolvent away, and distilling the residue in vacuo.
 3. A solution ofstarting material for MOCVD, comprising at least 10 wt % organic solventadded to tantalum tertiary amylimido tris(dimethylamide).
 4. A method offorming a tantalum nitride film by the MOCVD method wherein tantalumtertiary amylimido tris(dimethylamide) is used as the starting material.